Some power supply apparatuses that include a plurality of battery modules perform a protection process of electrically separating from the power supply apparatus a battery module in which an abnormality has occurred. A break in a voltage detection line between a battery and a voltage detecting unit, and overcharging or overdischarging of a battery, may be types of abnormalities of battery modules. See, for example, patent documents 1-4.
However, in a case where the same protective process is performed for all abnormalities that occur in a battery module, a power supply apparatus may possibly be excessively protected through separation of another battery module that does not need to be separated, or the same abnormality may occur in another battery module later, i.e., the power supply apparatus may be insufficiently protected.